The invention relates to an electron optical inspection apparatus for sample inspection and defect review in semiconductor manufacturing and the like. However, it would be recognized that the invention has a much broader range of applicability.
All the way through, during the fabrication processes of semiconductor devices such as integrated circuits (ICs) and memory devices, the defects inevitably existed on the wafer, even on the reticle or mask, keep impacting the yield of products, and thus the measure regarding to the detection of defects is supremely demanded. Prior to the sub-micron age, the optical inspection tools were the significant means to detect the defects on the wafer. However, with the narrowing dimension of the semiconductor devices, the conventional optical inspection tool was thrown into a dilemma for the dimension of defects became smaller than its optical wavelength to probe defects. On the other hand, with the progress of the semiconductor fabrication, the multi-layer architecture is built on the semiconductor wafer, in which insulating layers and interconnects are between interconnect layers. In such a manner, some kind of new types of defects, such as lower defects appeared in the interconnect layers and interconnects, occur and are impossible to be observed by the optical inspection tools. For example, in the dual damascene process, Via etching and Cu filling cause the killer defects like etching residual defects, voids, voltage-contrast type defects (e.g. electrical shorts or open at contacts), etc. which make us require a different means from the optical inspection tool to find them for their hiding places inside the damascene structure. Therefore, the e-beam inspection tools turn out to be the only means in response to the prompt demand on the less than submicron defects and the new type defects for their unique characteristics.
In the technical aspect, the e-beam inspection applies the beam current to probe the select part of wafer and detects signal electrons (e.g. secondary electrons, back scatter electrons and Auger electrons) from it so that the image is collected. And for the optical inspection tools, it is the measurement of light reflected from the surface of sample. Between them, the throughput gap is the mainly distinction, and in addition, it can also see why the optical inspection can only detect defects on the surface for the reflected light being from the sample surface. To fill the gap, the industry has been working on the e-beam inspection tools with the large field and large beam, further, on the multi-beam inspection tools. However, the e-beam inspection tool with the large field and large beam has a disadvantage that the off-axis aberrations are large and the resolution refers to be lower which leads to finely analyze defects being limited. Consequently, in a practical way, two types of e-beam inspection tools were employed for the wafer inspection in turn to improve the throughput. The first used e-beam inspection tool is called the EB inspection for finding the region of interesting (or hot areas), which means the possible areas defects existed, on wafer. The EB inspection is an e-beam inspection tool with both of large field and large beam, and hence it has a faster scanning speed but a lower resolution. It cannot meet the requirement of the high resolution, so what it can do is to mark the region of interesting rather than analyze the defects. The second one is called the EB review (also named Review SEM) for finely analyzing defects based on the image data from the EB inspection instead of scanning the whole wafer to find defects. The small scanning field, the small beam and the high resolution feature the EB review which has a poor throughput. As mentioned above, the examination of wafer defects includes two steps: the first one is “the inspection”, that is, the EB inspection is used to help find the region of interesting. The second one is considered as “the review”, namely, the EB review is adopted to further analyze defects. In the way, the throughput can be promoted due to at first we approximately make sure the positions of defects, after that do analysis of defects on these positions, which makes reviewing the entire wafer not required.
For the sake of farther saving cost and time, some prior arts have provided e-beam inspection tools including two modes of the inspection and the review (i.e., possessing dual function of the EB inspection and the EB review), in which the specimen can be inspected and reviewed in single inspection tool without two separate inspection tools, so as to get rid of extra stage moving, transfer or relocation. For instance, patents of U.S. Pat. No. 7,960,697, U.S. Pat. No. 7,759,653 and U.S. Pat. No. 8,164,060 have disclosed a type of scanning electron apparatus with inspection and review mode of operation. Taking U.S. Pat. No. 7,759,653 as an example of the configuration, the electron beam apparatus comprises a cathode 101, an anode 102, a condenser lens 103, an immersion objective lens 104, an in-lens detector 105 and a single deflector system 106 containing two deflectors for a large scanning field such as shown in FIG. 1. In these patents, the inspection mode and the review mode could be switched by selecting the different working mode of objective lens 104 and in-lens detectors 105 (i.e., their optimum condition for inspection mode and review mode of operation, respectively). Noted that whether the inspection mode or the review mode has no choice but to operate in a large scanning filed because the single one deflector system 106 for a large scanning filed is equipped with. However, it has a fatal flaw that an enlarged spot size is produced on the specimen while operating in the review mode acquired high resolution, because the deflector system 106 for a large scanning field is equipped with the high deflective sensitivity so that the noise from the deflector's driver (not depicted) strongly impacts the stability of the primary electron beam deflected. Besides, the single condenser lens 103 in these apparatus would make a limitation to select the size of the electron beam. In U.S. Pat. No. 6,841,776 disclosed by KLA-Tencor Technologies Corporation, as depicted in FIG. 2, it descripted an electro-optical apparatus with two subsystems for inspecting and reviewing, herein the inspection subsystem is performed while the substrate is on a continuously moving stage 205. The two subsystems share all electron optical elements in common, for example a cathode 210, a gun aperture 202, a beam aperture 203, an objective lens 204, a stage 205 and a detector system 206, etc., which makes it also hit the problem of satisfying the different demand of operating them.
Due to these problems, there is a need for a more reliable and accurate electron optical apparatus with two modes of operation which allows the two subsystems can functionally execute well, respectively, without the limits of the functional compatibility between the inspection mode of operation and the review mode of operation.